Multiple-speed photographic emulsion containing an organic compound oxidizable to a spectral-sensitizing dye

ABSTRACT

A MULTIPLE-SPEED PHOTOGRAPHIC EMULSION IS PROVIDED BY INCORPORATING A COLORLESS DYE PERCURSOR IN A PHOTOGRAPHIC SILVER HALIDE EMULSION. AFTER EXPOSURE, THE EMUSLION IS DEVELOPED AND A NORMAL PHOTOGRAPHIC IMAGE IS OBTAINED, DURING THE COURSE OF DEVELOPMENT, THE DYE PERCURSOR IS CONVERTED INTO AN ACTIVE SPECTRAL SENSITIZING DYE IN THE AREAS OF EXPOSURE. IF HIGHER PHOTOGRAPHIC SPEED IS DESIRED, THE ELEMENT IS THEN UNIFORMLY REEXPOSED TO RADIATION CORRESPONDING TO THE SENSISTIVITY OF THE SPECTRAL SENSITIZING DYE AND DEVELOPMENT IS CONTINUED TO OBTAIN AN AMPLIFIED IMAGE CORRESPONDNG TO A RELATIVELY HIGHER SPEED.

United States Patent 3,796,579 MULTIPLE-SPEED PHOTOGRAPHIC EMULSION CONTAINING AN ORGANIC COMPOUND OXI- l ggz mm TO A SPECTRAL-SENSITIZING Leslie G. S. Brooker, deceased, late of Rochester, N.Y., by Lincoln Rochester Trust Company, executor, and Paul B. Gilman, Jr., Rochester, N.Y., assignors to Eastman Kodak Company, Rochester, NY. No Drawing. Filed Apr. 10, 1972, Ser. No. 242,737 Int. Cl. G03c 1/02 U.S. Cl. 96-94 R 16 Claims ABSTRACT OF THE DISCLOSURE A multiple-speed photographic emulsion is provided by incorporating a colorless dye precursor in a photographic silver halide emulsion. After exposure, the emulsion is developed and a normal photographic image is obtained. During the course of development, the dye precursor is converted into an active spectral sensitizing dye in the areas of exposure. If higher photographic speed is desired, the element is then uniformly reexposed to radiation corresponding to the sensitivity of the spectral sensitizing dye and development is continued to obtain an amplified image corresponding to a relatively higher speed.

This invention relates to photography and more particularly to a novel multiple-speed photographic emulsion.

Normally, photographic emulsions have fixed or limited exposure latitude depending on the nature of the photographic emulsion, the type of energy to which it is exposed or the manner in which it is processed.

A typical black-and-white photographic emulsion has an exposure latitude of about two stops (a factor of 4). Such fil'm must, therefore, be correctly exposed. Any miscalculation in presetting the camera controls will result in either underor over-exposure of the film. A drastic miscalculation in exposure can result in unusable negatives.

Photographic materials with extended exposure latitude have been known. Such materials comprise multiple-layer coating with color couplers which are incorporated in the various speed silver halide emulsions. They are printed through selected complimentary filters. These filters make visible the image of a given color layer so that the layer which has received the proper exposure may be selected for printing. Such elements are disclosed, for example, in U.S. Pat. 3,450,530.

Other techniques have been described to amplify the initial response of a developing grain, such as by using the iodide ion released during development of a multilayer film to trigger development of internally fogged grains in another layer. This technique is described in Luckey et a1. U.S. Pat. 2,996,382.

Although prior-art image-amplification techniques of the type indicated have olfered a number of advantages, they have had certain drawbacks, particularly in the expense and difficulty of manufacture of the multiple-layer elements.

Accordingly, it is an object of this invention to provide novel multiple-speed photographic materials. Another object is to provide a novel photographic emulsion containing an incorporated sensitizing dye precursor. Still another object is to provide a method for amplifying photographic images and thereby increasing the speed of the photographic element. Another object is to provide a photographic element which can vary considerably in speed depending on whether or not the element is exposed a second time during or after the development step. It is still a further object of this invention to provide a method by which the oxidation products of photographic develop- ICC ment convert a colorless dye precursor into an active spectral sensitizer in an imagewise pattern which will result In photographic amplification when development takes place under minus blue light. Other objects will be apparent from the following specification and the appended claims.

These and other objects are obtained by our novel photographic emulsions, elements and methods of processing which provide for the amplification of the image of a photographic, spectrally unsensitized silver halide emulsion which has been exposed in the usual manner. The photographic element of the invention contains a sensitizing dye precursor. During development, the colorless dye precursor which is incorporated in the emulsion becomes oxidized to a sensitizing dye. This sensitizing dye, liberated at the site of development, becomes attached to a nearby silver halide grain and spectrally sensitizes it. If this development has been carried out in total darkness, the emulsion can then be uniformly exposed to light of a color which will not affect the unsensitized grains but will affect the sensitized grains, after which it is developed a second time to amplify the original image. In an alternative procedure, the first development can be carried out under yellow safelights so that as soon as the sensitizing dye is formed, the dye sensitizes neighboring grains which immediately undergo development to produce an amplified image. I

In accordance with the present invention, we have provided a novel silver halide emulsion and photographic element which can be processed to diiferent photographic speeds in a simple, quick and inexpensive manner. The processing enables the photographic element to be developed to a selected photographic speed by a choice of developing conditions.

The novel multiple-speed photographic emulsion comprises a photosensitive silver halide, a mordanting agent and a colorless dye precursor which is oxidizable by an oxidized photographic developing agent to form in situ a dye which spectrally sensitizes the silver halide to radiation of a region of the spectrum other than the sensitivity of the emulsion prior to oxidation of the dye precursor. For example, the photosensitive silver halide can have only native sensitivity (i.e., to ultraviolet and far blue light) and the sensitizing dye formed during development can sensitize the undeveloped silver halide to the green region of the visible spectrum. As another example, the silver halide can be sensitized to the red region of the visible spectrum and the sensitizing dye formed during development can sensitize the undeveloped silver halide to the green region of the visible spectrum. The photographic element of the invention comprises an emulsion of this type coated on a support.

The method of the invention in general comprises (a) imagewise-exposing the element to radiation of the electromagnetic spectrum to form a latent image in the radiation-struck areas, (b) developing the latent image in the dark, whereby the oxidation products of the photographic development convert the colorless dye precursor contained in the emulsion to a sensitizing dye which is adsorbed by the adjacent silver grains in an imagewise pattern, (c) exposing the photographic element to uniform illumination with light which will be absorbed by the silver halide spectrally sensitized with the sensitizing dye formed during development (the silver grains not so spectrally sensitized will not be aifected by this illumination), and (d) redeveloping the grains exposed during (0) above to allow a secondary stage of photographic amplification to take place by converting the imagewise spectrally sensitized, silver halide grains to metallic silver.

Insayingthat we subject the photographic element to uniform illumination in exposing it for the second time, we use the term uniform to distinguish from imagewise exposure and do not mean to exclude the possibility of using the well-known processing techniques of burning in or dodging, by means of which areas of overor under-exposure can be compensated for by giving a more intense or less intense second exposure to such areas.

Optionally, the first development may be carried out under uniform illumination with light of a color not absorbed by the spectrally unsensitized silver halide crystals, but which is absorbed by the spectrally sensitized silver halide crystals formed during development. The development reaction provides an imagewise pattern of spectralsensitizing dye which is adsorbed by the adjacent silver halide grains, and said grains will immediately become developable as they are exposed during the development step.

Photographic elements prepared according to this invention can be processed by various methods including processing in alkaline solutions containing conventional developing agents such as hydroquinones, catechols, aminophenols, 3-pyrazolidones, phenylenediamines, ascorbic acid derivative, hydroxylamines, hydrazines, reductones and the like; web processing such as described in Tregillus et al. US. Pat. 3,179,517; stabilization processing as described in Russell et al. Stabilization Processing of Films and Papers, PSA Journal, vol. 16B, August 1950; monobath processing as described in Levy Combined Development and Fixation of Photographic Images with Mono baths, Phot. Sci. and Eng, vol. 2, No. 3, October 1958 and Barnes ct al. US. Pat. 3,392,019. If desired, the photographic elements of this invention can be processed in hardening developers such as those described in Allen et al. US. Pat. 3,232,761; in roller transport processors such as those described in Russell et al. US. Pat. 3,025,- 779; or by surface application processing as described in Example 3 of Kitze US. Pat. 3,418,132.

Particularly good results are obtained when the emulsions of the photographic elements of this invention con tain an incorporated ballasted developing agent such as the ballasted hydroquinones, e.g., t-butyl hydroquinone. The use of incorporated ballasted developing agents reduces the migration of the oxidized developing agent from the sites of exposure and development. This thereby reduces the formation of the sensitizing dye away from the sites of development and produces a sharper amplified image. For best results the emulsion should contain a quantity of ballasted developing agent at least sufficient to completely develop all the silver halide of the emulsion if it were completely fogged. The exposed element is then processed by being contacted with an alkaline solution similar to the usual developer solutions except that the solution does not contain a developing agent.

The colorless dye precursor component of the photographic element of this invention is a compound of the formula.

(I) Z1 Z1 and is present in an amount sufficient to yield upon oxidation by oxidized developer products in the time required for development of the element a sensitizing amount of a dye of the formula:

=CHC=CH In the above Formulae I and II:

atoms in the alkyl moiety (e.g., benzyl, fi-phenylethyl, w-phenylbutyl, etc.), a sulfoalkyl group, preferably sulfo lower akyl containing from 1 to 4 carbon atoms in the alkyl moiety (e.g., 2-sulfoethyl, 3-sulfopropyl, 3-sulfobutyl, 4-sulfobutyl, etc.), a carboxyalkyl group, preferably a carboxy lower alkyl containing from 1 to 4 carbon atoms in the alkyl moiety (e.g., 2-carboxyethyl, 3-carboxypropyl, 4-carboxybutyl, etc.), a sulfatoalkyl group, preferably a sulfato lower alkyl containing from 1 to 4 carbon atoms in the alkyl moiety (e.g., 2-sulfatoethyl, 3-sulfatopropyl, 4-sulfatobuty, etc.), an alkoxyalkyl group, preferably lower alkoxy lower alkyl containing from 1 to 4 carbon atoms in both the alkoxy and alkyl moieties (e.g., 2- methoxyethyl, 3-methoxypropyl, 4-propoxybutyl, etc.), an acyloxyalkyl group, preferably acyloxy lower alkyl containing from 1 to 4 carbon atoms in the alkyl moiety (e.g., acetyloxyethyl, propanoyloxyethyl, butanoyloxybutyl, benzoyloxyethyl, tolyloxypropyl, etc.), an alkoxycarbonylalkyl group, preferably lower alkoxy carbonyl lower alkyl containing 1 to 4 carbon atoms in both the alkoxy and alkyl moieties (e.g., 2-methoxycarbonylethyl, 4-ethoxycarbonylbutyl, 2 butoxycarbonylethyl, etc.), a dialkylaminoalkyl group, preferably di-lower alkylamino lower alkyl containing 1 to 4 carbon atoms in the alkyl moieties (e.g., dimethylaminoethyl, diethylaminopropyl, diethylaminobutyl, etc.), a cycloaminoalkyl group, preferably cycloamino lower alkyl containing 4 to 6 atoms in the cycloamino moiety and 1 to 4 atoms in the alkyl moiety (e.g., l-pyrrolidinylethyl, 4-morpholinopropyl, l-piperidinobutyl, 2-pyrrolin-1-ylmethyl, etc.), an alkenyl group, preferably lower alkenyl containing 2 to 4 carbon atoms, (e.g., allyl, l-propenyl, l-butenyl, 2-butenyl, etc.), or an aryl group including substituted aryl (e.g., phenyl, naphthyl, tolyl, xylyl, halophenyl such as p-chlorophenyl, p-bromophenyl, 2,4-dichlorophenyl, alkoxyphenyl such as methoxyphenyl, etc.);

(b) R represents hydrogen, an alkyl group, preferably a lower alkyl group containing from 1 to 4 carbon atoms (e.g., methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, isobutyl, tert-butyl, etc.) or an aryl group (e.g., phenyl, naphthyl, 4-t0lyl, 2-tolyl, 2,4-dimethylphenyl, etc.);

(0) each X represents an acid anion (e.g., halide such as chloride, bromide or iodide, p-toluenesulfonate, thiocyanate, sulfamate, perchlorate fluoborate, methylsulfonate, ethylsulfonate, fluorosulfonate, 2,4-dinitrobenzenesulfonate, etc.); and

((1) each Z represents the nonmetallic atoms necessary to complete a heterocyclic nucleus containing 5 to 6 atoms in the heterocyclic ring, which nucleus can contain a seond hetero atom such as oxygen, nitrogen, selenium or sulfur such as a thiazole nucleus (including substituted and unsubstituted benzothiazole and naphthothiazole nuclei and the like), e.g., thiazole, 4-methylthiazole, 4-phenylthiazole, 4,5-diphenylthiazole, 4-(2-thi* enyl)thiazole, benzothiazole, 4-chlorobenzothiazole, 4- methylbenzothiazole, 4 methoxybenzothiazole, 4-ethoxybenzothiazole, 4-phenylbenzothiazole, S-chlorobenzothiazole, S-bromobenzothiazole, S-methylbenzothiazole, S-methoxybenzothiazole, 5 ethoxybenzothiazole, S-phenylbenzothiazole, o-chlorobenzothiazole, 6 bromobenzothiazole, 6 methylbenzothiazole, o-methoxybenzothiazole, 6-ethoxybenzothiazole, S-methoxynaphtha [2,3-d]-thiazole, naphtho[2,l-d]thiazole, naphtho- [1,2-d] thiazole, etc.; an oxazole nucleus (including substituted and unsubstituted benzoxazole and naphthoxazole nuclei and the like), e.g., oxazole, 4-phenyloxazole, benzoxazole, 5-c'hlorobenzoxazole, 5-methylbenz oxazole, 5-bromobenzoxazole, 5 methoxybenzoxazole, S-ethoxybenzoxazole, S-phenylbenzoxazole, S-methoxynaphth[2,1-d]oxazole, etc.; a selenazole nucleus (including substituted and unsubstituted benzoselenazole and naphthoselenazole nuclei and the like), e.g., selenazole, 4-methylselenazole, 4-nitroselenazole, 4-phenylselenazole, benzoselenazole, 5 chlorobenzoselenazole,

0.2 grami 1-phenyl-3-pyrazolidone -6 chlorobenzoselenazole; naphtho[2,1-d] selena z ole, t -i a d a -q inel ne. nu l s. (ea. r u eq ne ethyI-Z-quinoline, 6. 7 ch1oro 2-quinoline, 8 chIOr o-Z quinoline, 4-methoxy-2-quinoline, 8 hyd r oxy-2-qu ino- I a. .1 Typical dye precursors represented by FormulaI' above include: I (A) 2,2'-trimethylenebis- (3. ethylbenzo'thiazolium per- H chlorate); I (B) 2,2'-trimethy1enebis -"(3 methylben zoxaz I .dide); I .1 I I (C) -2,2 '-trimethylenebis-(3\ ethylbenzose le niu m p-tolu- .enesulfonate); and IQII, I (D) 2,2'-trimethylenebis-(1' methylquino ne perchlo- -rate). f

The novel photographic emulsions of tl 'lisinvent ioncan be made by any of the well-known emulsionqnaking techniques in which" the various components such' 'asthe vehicle, e.g., gelatin, the silver salt "and other' addenda are blended together. A' suitable concentration of dye precursor is from 3 to '1000'mg. of dye precursor per inole of silver with the preferred'range being from 50 to 400 mg. of dye precursor per moleof silver. f f

In preparing the photographic elements of'the invention, the emulsions containing the dye precursor are coated on a support such as film, glassor paper in amounts of 50. to 500mg. Ag/ft? and p'referablygin amounts of 100 to 250 mg. Ag/ft. of support.

The following examples provide further understanding of the invention:

' {EXAMPLE i To 100 ml. of 5% aqueous gelatin solution is added40 grams of silver iodobromide emulsion containing 100 grams of gelatin (1.36 kg. 'of emulsion per mole of silver), 2 ml. of a 7 /2% 'saponin solution and 0.5 ml. of a 10%.formaldehyde solution. 1 I To ml. samples of this inixt'ureare added;

Sample 1. Control, no addenda, Sample 2. 2.0 ml. of a methanolic solu tion;containing in I ml., 20 mg. of the compound, 2,2' -trimethylene-bis- (3-ethylbenzothiazolium perchlorate).

The above two: emulsion s I II t I terephthalate support at et tbicknessand dried;

The dried oa n twxb sdfo' V? s nslt n millimeter slit width in a Bapsch and l ombspectrograph.

The film is then processed for 2 minutesiatflb f F inthe following developer solution:

190.0 ml. distilled water 1 sulfate 0.2 gram" N-methyl-p-aminophenol 10.0 ml. of 2.5 N sodium hydroxide," results: 1

I Relati ve'speeds I, I. No lights yeuow'ngn Samplel(control) 5140 40 J-' Sample 2 incorporate d dye precursor)" 160 I 320 filter to remove the ,1

In the dark; the inco p r t d quatfimarylsial-t'iamably l This speed gain is realized along with considerable image spreading, presumably due to the mobility of the releasedsensitizing dye or of the oxidized developer.

EXAMPLE 2 In order'to decrease the" mobility of the imagewise-released sensitizing dye, a developing agent (t-butylhydroquinone) is incorporated in the photographic emulsion. Solutions used in this preparation and/or in preparing a control emulsion are as follows:

Solution (1):

To 100 ml. of a 5% gelatin solution is added 42 grams of a silver iodobromide emulsion (0.3g cubes, sulfur plus gold sensitized and containing --80 grams of gel and 2.16 kg. emulsion per mole of silver), 2 ml. of a 7 /2% saponin solution and 0.5 I ml. of a 10% formaldehyde solution. Solution (2):

"A developer-gelatin mixture is prepared by dissolving 2 grams of t-butylhydroquinone in 18 ml. of methyl alcohol and pouring this solution, while I stirring, into 80 ml. of a 10% aqueous gelatin solution. 7 Solution (3):

A solution of the 2,2'-trimethylenebis-(3-ethylbenzo- I thiazolium perchlorate) is made by dissolving 0.1 gram of the material in 100 ml. of methyl alcohol. Two emulsion coatings are prepared as follows: Coating A: I To 10 ml. of solution (1) is added 4.3 ml. of solution ,(2) and a 5% gelatin solution to make a total of 15 ml. Coating B:

' I To 10 ml. of solution (1) is added 0.7 ml. of solution (3) and 4.3 ml. of solution (2).

- Coatings with .004" Wet thickness are made on subbed polyethylene terephthalate film support.

.The .dried coatings are exposed for ,4 of a second with a one=millimeter slit width in a Bausch and Lomb spectrograph. These coatings are processed for 2 minutes in the following solution at F.

Distilled water m1 200.0 2.5 N sodium hydroxide ml 10.0 Sodium sulfite "gram-.. 1.0 Potassium bromide gram 0.5

f The results are as follows:

Relative speeds N0 lights Yellow lights Coating A (incorporated developer only). 80 Coating B (incorporated dye precursor and 80 3 0 developer)--.

- EXAMPLE 3 This example illustrates a further procedure for confining the development-released products by adding an extremely fine-grain Lippman emulsion with alarge surface area that is; capable of more eifectively mordanting the released, sensitizing dye. This is accomplished as follows: "t iTo ml.- of a 5% gelatin solution is added 21 grams of a silver bromoiodide emulsion (as described in Exam- .ple 2) and 21 grams of a very fine-grain Lippman-type emulsion containing 60 grams of gelatin and 2.14 kg. of emulsion per mole of silver.

1To 100 ml. of the above preparation is added 6.8 ml. of a 0.1% methanolic solution of 2,2'-trimethylenebis-(3- ethylbenzothiazolium perchlorate 43.2 ml. of a developer solution containing 2 grams of t-butylhydroqui-- none,- 18 ml. methyl alcohol and 80 ml. of 10% gelatin,

Relative speed a.

No lights Yellow lights Emulsion with incorporated developer and dye precursor 40 160 The above examples illustrate the ability of an oxidizable dye precursor, when incorporated in a silver halide photographic emulsion, to amplify the latent image thereby providing a photographic element of various sensitometric speeds.

The photographic layers used in the 'practice of this invention may be coated by various coating procedures including dip coating, air knife coating, curtain'coatiiig 'or extrusion coating using hoppers of the type described in Beguin U.S. Pat. 2,681,294. If desired, two or more layers may be coated simultaneously by the procedures described in Russell U.S. Pat. 2,761,791 and Wynn British Pat. 837,095. This invention also can be used for-silver halide layers coated by vacuum evaporation as described in British Pat. 968,453 and LuValle et al. U.S. Pat. 3,219,451.

The photographic layers and other layers of a' ph otographic element employed and described herein can be T coated on a wide variety of supports. Typical supports include cellulose nitrate film, cellulose ester filmgwpoly- (vinyl acetal) film, polystyrene film, poly(ethylene tere;-' phthalate) film, polycarbonate film and relatedfilmsior resinous materials, as well as glass, paper, metal and the like. Typically, a flexible support is employed, especially a paper support, which can be partially r-acetylated or coated with baryta and/or an alpha-olefin,v polymer, par;- ticularly a polymer of an alpha olefin containing 210 10 carbon atoms such as polyethylene, polypropylene, ethyl} ene, ethylenebutene copolymers and'the like.

The silver halide emulsions used with this invention may be unwashed or washed to remove soluble salts. In the latter case, the soluble salts may be removed by chillsetting and leachingor the emulsion may --be-coagulation washed, e.g., by the procedures described in Hewitson et al. U.S. Pat. 2,618,556; Yutzy et a1. U.S. Pat. 2,614,928; Yackel U.S. Pat. 2,565,418;'Harf et'al. U.S."Pat.f3 24 1j,'- 969 and Waller et al. U.S. Pat. 2,489,341. .The silverzhalide emulsions used, in accordance this invention can comprise, for example, silver chloride, silver bromide, silver bromoiodide, silver chlorobrom'ide, silver chloroiodide, silver chlorohromiodider: crystals or mixtures thereof. The emulsions may be coarse or fine grain emulsions prepared by any of the well-known techniques, e.g.,- single jet emulsions such as those described in Trivelli and .Smith The Photographic Journal,. rvol. LXXDC, May 1939, (pp. 330-338), double-.jet' e'mulsions such as Lippmann emulsions, ammoniacal emulsions, thiocyanate or thioether ripened emulsions such asthosedescribed in Netz et al. U. S. Pat. 2,222,264;" Illingsworth U.S. Pat. 3,320,069; and McBride U.S. Pat; 3,271,157 Surface image emulsions may be used or internaltimage emulsions may be used such as those described in Davey et al. U.S. Pat. 2,592,250; Porter et al. U.S. Pat'."- 3',2 06',"- 313 and Bacon et al. U.S. Pat. 3,447,927. If desired, mixtures of surface and internal image emulsionsrnay' be used as described in Lucky e t al. U.S. Pat 2,99eg3s25r11e emulsions may be regular grain emulsions such as thetype described in Klein and Moisar, J. Phot. Sci., vol. 12,"No.

5, September/October1'964,"'ppi 242-251, Negative type etnuls'ions may be used (indirect-positiveemulsions may be used such as those described in Leemakers U.S. -Pat. 2,184,013; Kendall "'etal. U.S. Pat. 2,541,472; Berr'inian U.S. Pat. 3,367,778; Schouwenaars British Pat. 723,019; Illingsworth et al. French Pat. 1,520,821; Ives U.S. Pat. 2,563,785; Knott 'et al. U.S. Pat. 2,456,953 and Land Isl t- .8 1.8

The photog'raphic and other hardenable layers used in the practice of this invention can be hardened by various organic or inorganic hardeners, alone or in combination, such as the aldehydes and blocked aldehydes, 'ketones, carboxylic ana'earbeaiaaeid derivatives, sulfonate esters, sulfonyl halides and vinyl sulfonylethers, active halogen compounds epoxy coir'ipounds, 'aziridines, active olefins, isocyanates, carboimides, and polymeric hardeners such as oxidized;- polysaccharides likedialdehyde starch and v ua e m nd e r Thephotographic emulsionsand elements described in the practice of this invention can contain various colloids alone or in combination as vehicles, binding agents and various layers. Suitable hydrophilicmaterials include both naturally-occurring substances such as proteins, for example, gelatin, gelatin derivatives, cellulose derivatives, polysaccharides such as de xtra n, gum arabic and the like; andsynthetic polymeric substances such as water-soluble polyvinyl. compounds like poly(vinylpyrrolidone), acrylamide polymers and the like.

The described photographic emulsion layers and other layers of a photographic element employed in the practice of this invention can also contain alone or in combination with hydrophilic, water-permeable colloids, other synthetic polymeric compounds such as dispersed vinyl compounds such as in latex form and particularly those which increase thedimensional stability of the photographicl materials; 3 Suitable fsynthetic polymers include those described, for example 'jn Nottorf U.S. Pat. 3,142, S68'issi1ed 'July' 28', 1964;'White,IJ.S. Pat. 3,193,386 issued July 6, 1965;.Houcket,alL,U.S. Pat. 3,062,674 issued Nov. 6, 1962; Houck et al. U.S."P'at. 3,220,844 issued Nov. 30, 1965; Ream et al. -U';S.Pa.t 3,287,289 issued Nov; '22, 'l 966- -and 'DykStra -ULS. Pat. 3,411,911 issued Nov.*19," 1968; particularly "effective are those water-insoluble polymers:of alkyl acrylates and methacrylates, acrylic acid, sulfoalkyl acrylates or methacrylates, those which have cross-linking sites which facilitatehardening or curing atld thosewhaving recurringsulfobetaine units as described in Dykstra Canadian Pat. 774,054.

The photographic elements used with this invention may contain aptistatic or conducting layers, such layers may'xcomprise soluble salts, eig'.,'chlorides, nitrates, etc.,

metal. layer s, ionic polymers such as those de- Mi'fisk LhS. Pat. 2, 86'1,05 6"and Sterrnan et al. 206, 12'2162' insoluble inorganic salts such as a n I bed in TrevoyUSfPat. 3,428,451. flhelph'otographic layers employed in 'the practice of this invention can-contain plasticizers and lubricants such as polyalcohols, e.g., glycerin" and 'diols of the'type described in Milton et al. U.S. Pat. 2,9 6 0,404; fatty acids or esters such as those described in Robijns U.S. Pat 2,588, 765 and man ges, gat.',3,l2;l,Q60 andgsilicone resins su h-flatness esc ilisdi rll Pen h-P t- 5,0 1-

The photographic layersemployed in the practice of this invention may contain surfactants such as saponin; *anioaig cornpou ndssuch as thealkyl' aryl suifonates de 'in Bald'siefen U.S. Pat. 2,600,831; amphoteric is s qhl a hose. .dsesr hed-..in B Ezra.,.U-S.

1 5i. 3,133,816 and water-solu e adducts of'glycidol and .alkylphenolusuehtas .thoseldescribed in, olin' Mathieson British Pat. 1,022,878.

""Z' The photographic elements-employed in" the practice ofthisinvention iiiaycontain matting agents'sucli as s'fafchi titanium dioxide} 'Zitic -oxide,{ silica; polymeric beads including lieads'of the type describedi n' 'Jelley et a1. U.S. Pat. 2,992,101 and Lynn'USJPat. 2,701,245.

The photographic elements used in this invention may contain brightening agents including stilbenes, triazines, oxazoles and coumarin'brightening agents. Water soluble brightening agents may be used such as those described in Albers et al., German Pat. 972,067 and McFall et al. U.S. Pat. 2,933,390 or dispersions of brighteners may be used such as those described in Jansen German Pat. 1,150,274, Oetiker et al. U.S. Pat. 3,406,070 and Heidke French Pat. 1,530,244.

Spectral sensitizing dyes can be used conveniently to confer additional sensitivity to the light-sensitive silver halide emulsion of the multilayer photographic elements of the invention. However, as we have indicated, any spectral sensitizing dye included with the colorless dye precursor must not sensitize in the area of the electromagnetic spectrum where the dye formed from the colorless dye precursor by oxidized developer absorbs radiation. For instance, additional spectral sensitization can be obtained by treating the emulsion with a solution of a sensitizing dye in an organic solvent or the dye may be added in the form of a dispersion as described in Owens et al. British Pat. 1,154,781. For optimum results, the dye may either be added to the emulsion as a final step or at some earlier stage.

Spectral sensitizers which can be used include the cyanines, merocyanines, complex (tri or tetranuclear) merocyanines, complex (tri or tetranuclear) cyanines, holopolar cyanines, styryls, hemicyanines (e.g. enamine hemicyanines), oxonols and hemioxonols.

Dyes of the cyanine classes may contain such basic nuclei as the thiazolines, oxazolines, pyrrolines, pyridines, oxazoles, thiazoles, selenazoles and imidazoles. Such nuclei may contain alkyl, alkylene, hydroxyalkyl, s-ulfoalkyl, carboxylalkyl, aminoalkyl and enamine groups and may be fused to carb-ocyclic or heterocyclic ring systems either unsubstituted or substituted with halogen, phenyl, alkyl, haloalkyl, cyano or alkoxy groups. The dyes may be symmetrical or unsymmetrical and may contain alkyl, phenyl, enamine or heterocyclic substituents on the methine or polymethine chain.

The merocyanine dyes may contain the basic nuclei mentioned above as well as acid nuclei such as thiohydantoins, rhodanines, oxazolidenediones, thiazolidenediones, barbituric acids, thiazolinones and malononitrile. These acid nuclei may be substituted with alkyl, alkylene, phenyl, carboxyalkyl, sulfonalkyl, hydroxyalkyl, alkoxyalkyl, alkylamino groups or heterocyclic nuclei. Combinations of these dyes may be used, if desired. In addition, supersensitizing addenda which do not absorb visible light may be included, for instance, ascorbic acid derivatives, azaindenes, cadmium salts and organic sulfonic acids as described in McFall et al. U.S. Pat. 2,933,390 and Jones et al. U.S. Pat. 2,937,089.

The sensitizing dyes and other addenda used in the practice of this invention may be added from water solutions or suitable organic solvent solutions may be used. The compounds can be added using various procedures including those described in Collins et al. U.S. Pat. 2,912,- 343; McCrossen et al. U.S. Pat. 3,342,605; Audran U.S. Pat. 2,996,287 and Johnson et al. U.S. Pat. 3,425,835.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be efiected within the spirit and scope of the invention.

We claim:

1. A photosensitive silver halide emulsion containing a colorless organic compound having the following formula:

which is oxidizable by an oxidized photographic developing agent to form in situ a sensitizing amount of a spectralsensitizing dye having the formula:

wherein (a) each R represents an alkyl group having from 1 to 18 carbon atoms, a phenyl group, a substituted phenyl group, a naphthyl group, a substituted naphthyl group or an alkenyl group, (b) R represents hydrogen, a lower alkyl group, a phenyl group, a substituted phenyl group, a naphthyl group or a substituted naphthyl group, (c) X represents an acid anion and (d) each Z, represents the non-metallic atoms necessary to complete a heterocyclic nucleus containing 5 to 6 atoms in the heterocyclic ring, in the time required for development of the emulsion by said agent.

2. A photosensitive silver halide emulsion containing a colorless dye-precursor compound of the formula:

said compound being present in an amount suflicient to yield upon oxidation a spectrally sensitizing amount of a dye of the formula:

wherein (a) each R represents an alkyl group having 1 to 18 carbon atoms, a phenyl group, a substituted phenyl group, a naphthyl group, a substituted naphthyl group, or an alkenyl group, (b) R represents hydrogen, a lower alkyl group, a phenyl group, a substituted phenyl group, a naphthyl group or a substituted naphthyl (c) X represents an acid anion and (d) each Z represents the nonmetallic atoms necessary to complete a heterocyclic nucleus containing 5 to 6 atoms in the heterocyclic ring.

3. An emulsion according to claim 2 wherein each Z represents the nonmetallic atoms necessary to complete a heterocyclic nucleus selected from the group consisting of a thiazole nucleus, an oxazole nucleus, a selenazole nucleus and a 2-quinoline nucleus.

4. An emulsion according to claim 2 in which said dye-precursor compound is 2,2'-trimethylenebis(ES-ethylbenzothiazolium perchlorate).

5. An emulsion according to claim 2 which is free of sensitizing amounts of dyes that spectrally sensitize to the same wavelength as the dye to which said dye-precursor compound sensitizes when it is oxidized.

6. An emulsion according to claim 2 which also contains a mordant for the dye formed by oxidation of said dye-precursor compound.

7. An emulsion according to claim 6 in which said mordant is a fine-grain Lippmann emulsion which is admixed with the photosensitive silver halide emulsion in an amount sufiicient to inhibit migration of the sensitizing dye formed from said dye-precursor compound.

8. A photographic element comprising a support and an emulsion according to claim 1.

9. A photographic element comprising a support and an emulsion according to claim 2.

10. A photographic element comprising a support and an emulsion according to claim 3.

11. A photographic element comprising a support and an emulsion according to claim 4.

12. A photographic element comprising as support and an emulsion according to claim 5.

13. A photographic element comprising a support and an emulsion according to claim 6.

14. A photographic element comprising a support and an emulsion according to claim 7.

15. A photosensitive silver halide emulsion containing 2,2'-trimethylenebis(3-ethylbenzothiazolium perchlorate) 10 and t-butyl hydroquinone.

16. A photographic element comprising a support and an emulsion according to claim 15.

1 2 References Cited UNITED STATES PATENTS 3,498,785 3/1970 Bloom et al. 96-3 3,100,703 8/ 1963 Sprague et a1 96-33 2,104,064 1/1938 Zeh 96-133 ROLAND E. MARTIN, JR, Primary Examiner I. L. GOODROW, Assistant Examiner US. Cl. XJR. 9654, 137 

